Forced air heating apparatus



Nov. 20, 1951 c. w. CARLSON 2,575,907

FORCED AIR HEATING APPARATUS Filed Jan. 24. 1951 FROM .SUPPLY am vif/sad ,aaa

ca/rR/naR A/R RfruR/v latented Nov. 20,y 1951 UNITED STATES PATENT OFFICE "i FORCED AIR HEATING APPARATUS Charles W. Carlson, Chicago, Ill.

Application January 24, 1951, Serial No. 207,467

6 Claims.

My invention relates to an improvement in forced air heating apparatus, and more particularly to an improvement in the means for controlling a forced air heating apparatus of the class wherein cold fresh air is fan-supplied to an enclosed heating zone in which the air is rst preheatedto a selected temperature and then further yheated to a higher distribution temperature by steam radiators. The improved control means of my inventionhas particular utility in connection with the forced air heating apparatus commonly used in public schools and the like.

i The heating and Ventilating of school buildings, factories employing large numbers of people, and similar structures presents special problems in that the air within the occupied portions of the building tends to become rapidly contaminated with carbon dioxide, etc. because of the relatively large number of people breathing the air. Ithas been found that buildings of this type require a system of forced ventilation in which the amount of fresh air supplied can be controlled independently of wind or Weather in order that such buildings will be adequately ventilated. Such forced ventilation is generally carried out by the use of a plenum-type ventilation system in which the air is forced into the rooms to be ventilated under slight pressure, thus causing the foul air to be discharged from the rooms. Ventilation systems of this type are generally combined with a forced air heating system in which the air for ventilation also carries the heat required to maintain a. comfortable temperature in the rooms. Indirect heating systems of this type are commonly foundin school buildings and are generally referred to as forced air or hot blast heating systems.

In order to understand the nature of my invention, it will be necessary to briefly describe the general nature of these forced air heating systems with which my invention has its greatest utility and importance. In general, cold fresh air is fan-supplied through a fresh air shaft to a heating zone or chamber containing steam radiators. This chamber or zone may take the form o f a room, tunnel, etc. but al1 of such heating *zonesl are characterized by having both preheating or tempering radiators and secondary or reheating radiators. Thus, in operation the fresh air which may be combined with recirculated air from in-V side the building is first preheated to a selected temperature and then further heated to a higher disposition temperature. After passing through this heating zone the heated air is then carried to the rooms to be heated and introduced into them, and thereby causes the foul air in the rooms the air to temperatures ranging between 75 andv 150 F. depending on variations in the heat re-V quirements of the rooms because of differing outside temperatures, wind conditions, etc. `l'or4 most buildings similar to public school buildings,

it has been found that in order to maintain a room temperature of around 70 F., it is necessary to deliver heated air to the rooms at considerably higher temperatures. For example, in mild weather the heated air can be delivered to the rooms at around '74 F., while in cold weather it can be delivered as high as 150 F. It will readily be understood that in order to maintainv the desired temperatures of the heated air that control means will be required for regulating the amount of heat transferred to the incoming air by the steam radiators within the heating chamber.

y of fresh heated air is continually delivered, to the air heating systems of the type described. above now utilize a damper located in a by-pass*'ii1ct'-l Hot blast heating systems of the plenum or tunnel type are usually operated so that a supply i .opens the iother oneY closes. ,1a. constant quantity of air to the room heating rducts, but controls the proportions of reheated around the preheatlng radiators which is opened and closed by a motor Which is responsive to a thermostat actuated by the temperature of the preheated air. Thus, with this control device when the tempered air temperature becomes higher than a selected value, the by-pass damper begins to open and allow a portion of the fresh cold air to be passed around the preheating radiators and then recombined with the air passing through the preheating radiators to achieve a cooling of the preheated air. If the temperature of the preheated air continues to rise further above the selected temperature setting, the thermostat causes the by-pass'damper to open further until a position is reached at which the proportion of by-passed air to preheated air is such as to hold the preheated air at the desired temperature. It has been found that such by-pass dampers provide a fairly effectiveV means for preventingthe temperature of the temperedv air from becoming excessive, but such by-pass dampers suffer from other serious defects which Will subsequently be discussed.

In addition t9 the by-pass damper around the preheaters just'described, substantially'all forced air heating systems of this type alsoutilize by` pass ducts around the secondary heaters and pro- Y vide mixing dampers to vary the proportions *of tempered by-passed air. and reheated air. These dampersrare generally constructed of two leaves J.andoperate so thatv as oneleaf leading to one duct This tends to admit land-"tempered air. These mixingv dampers are generally-,controlledby thermostats in the rooms z-tofbe. heatedwhich causeone leaf to be closed '.as.tl1e,v other opens in order to. deliver air to the mouth of the tunnel. Of course, the temperaturej increase will depend primarily on the steam pres-Y sure maintained within the reheating radiators. Forced air heating systems o the type described generally use two preheating radiators in order that one of the preheating radiators can be manually cut in and out of the heating circuit as the Y Outside air temperature requires. Also, these heating systems generally provide a plurality of reheating radiators, which may be arranged in series or in parallel, that is, the reheating radiators can be located so as to heatV divided portions of the tempered air to the temperature desired for particular rooms. Although such systems can be operated in a low pressure steam supply, it is common practice to utilize a high pressure steam supply at from 100 to 125 pounds per square inch gauge(p.s.i.g.).V When a highpressure steam supplyjisutilized, the rvsteamis passedy through a pressure regulating valve Aor device before being Y supplied to the radiation units. On the radiation roomatthe vtemperature required to produce the Y ,desired room temperature. seen, however, vthis ksecondary control means can .-do Anomore thanl cause all of the tempered air to ybe byapassed Whenthe room becomes 'overheated ,:Moreover, -it has been found advisable to fur- .ther` heat the tempered air by the reheating radi- :ators even though'it is not passed directly through .theseuradiators In other words, it is generally recommended that lthe 'tempered air temperature (produced by the preheating radiators be consider- "-reheating radiators. Since these casings and ducts-are constructed of metal and are'not provided With insulation, the temperature of the tempered' air Ycontinually rises as it is passed through the tunnel and around these casings because ofthe heat radiated through the casings by :the reheating radiators. Also, the reheating radiators radiate considerable heat, to the tempered fair passing through the by-pass ducts within the casings Injfact, it is not uncommon tov find in 'tunnel systems containing three of ,such casing istructures that the tempered air temperatureA is increased ,fromeight to twelve degrees as itis 'passed'Y along the tunnelaiter passing through the `reheatlng radiators whichare positionedlat .the

As can readily beV side of the system a pressure is generally maintanedof between one to three pounds, which can be varied according to heating requirements by :varying the setting of the pressure regulator. The

radiation unitsxare `connected in parallel to the steam supply and condensate return pipes are attached thereto. Both gravity and vacuum returns can be utilized, although the vacuum-type of rei"turniis'preferable The radiators (bothpreheatingrand reheating) are equipped With'manuallycontrolled gate valves by means of which the individual vradiators 'can be cut inor out ofthe system.v Thus, by manual 'adjustment iti .is-spose sible to vary the radiation capacity of the system and the pressure of the steam'supplied to the radiation units. l However, 'since both -the preheating and reheating `radiators are connected in parallel at any given'time or setting the'steam pressure tends to be substantially the same in all the radiation units. This has a'seriousdisadvantagexin producing overheating orV lunderheating-.5` asi' will subsequently be discussed. Y Also, it vis common practice to'introducefexhaust steam fromengines, etc. VVinto* the `radiation side of the system.

' 'Forced 'air heating systems of the type d'e- `scribed require the constant attention` of aheat- --ing engineer to adjust the manual controls in order to prevent underheating or overheating of 'the-lair: deliveredto the rooms. Even with constant attention the present control system for this type of heating apparatus is frequently' inadequate to prevent overheating or underheating of the air delivered to the rooms. The overheat#- `ing tends tol primarily Voccur in cold weather 'While theunderheating tends to occur in warm weather. AThis'is true'because the steam pressure required inthe preheating vradiators is determined by the outside temperature which` varies widely. pointed out above,.this same pressure is4 applied toV the reheating radiators whichare positioned .to heat the tempered'air even though most of itis ily-passedaround'the reheating radiators. Thus, when the preheating radiators contain suilicient steam pressure to warm the incoming airrom say 10? F. .to 70 F., the steam pressure in the reheating Vradiators will be such as to'overf .heaithel air .distributed totherooms. A further complication.` is thatthe individual rooms have ,varyingiheating requirements because ofdiier'- Vences inwind direction, radiation loss, etc. This meansthat frequently in order to sufcientlyheat some Vrooms vWhere .the lheat requirement is relatively greatV on the particularl day, it will be neef essary .tooverheatl other. rooms. y.Al-further .dis-

Asv

`'advantage 'o1' the present system is at high steam `pressure it is frequently necessary to spray water on the condensate return line above the condensate pump in order to condense the steam or further coolthe condensate. This is caused primarily in cold weather by the steam being forced through the reheating radiators without having `all-of the heat value utilized because of the excess steam pressure maintained on these units.

In warm weather the opposite condition tends `to prevail in that the air delivered to the rooms will frequently be underheated. This is true because the steaml pressure required in the preheating` radiators to meet the requirements of the incoming air is insuflicient at times for the reheatingradiators. Thus, except for a relatively narrow range of incoming air temperatures, the present systems tend to either over-radiate or under-radiate the air distributed to the rooms and are noteffective in spite of constant manual adjustment in regulating the distribution of steam by the reheating and preheating radiators.

A further serious defect of the present system is found in the use of a by-pass damper around the preheating radiators to control the tempered air temperature. In cold Weather, when the f tempered air temperature advances sufficiently` to cause the by-pass damper to open the rooms are caused to feel cold and drafty even though the temperature of the air Within the room remains relatively high. This effect is produced because the opening of the by-pass damper greatly reduces the air friction, and thereby increases the velocity of the air moving upwardly into the rooms. Immediately after the opening of the by-pass damper air at increased velocity is passed rapidly into the rooms at a considerably lower temperature than the air 'within the rooms, and thus causes the rooms to feed drafty and uncomfortable. to maintain an equilibrium temperature of the tempered air, the by-pass damper will continually be opening and closing throughout the heating period, it can be seen that the effect described is a rather serious disadvantage to the use of such a damper. Furthermore, in Warm weather the by-pass damper tends to open even though the reheating' radiators have insufficient steam pressure to meet the room requirements. In spite of these'disadvantages, until the present invention no one has suggested a satisfactory means for eliminating the mixing damper around the lpreheaters while maintaining an effective control of the tempered air temperature.

It is therefore an object of my invention to providezan entirely new means for controlling forced air heating systems of the type described in which overheating and underheating of the air is substantialy prevented, and the undesirable by-pass damper around the preheaters is eliminated. `It is a further object of my invention to devise a control means for use in forced air heating apparatus which will substantially decrease the manual adjustments required to deliver the air to the rooms at'proper temperatures, and to allowthe system to operate automatically after equilibrium conditions are established on a particular day. More specifically, it is an object of my invention to provide a control means of the type indicated which will decrease the amount of fuel required to satisfactorily heat a building, and which will prevent the rooms from periodically feeling drafty because of the introduction of cold air at increased velocity; In this connection, it is an object of vmy invention` to Ieliminate the by- When it is realized that in order pass mixing damper around the preheating radiators. It is a still further object of my invention to provide a new control means to accomplish the results indicated which can be installed in the forced air heating systems now in use with relatively little cost.

lIn place of the by-pass mixing damper and continual Vmanual adjustments as heretofore required, it is an object of my invention to provide control means which will automatically supply steam to the radiation units at the pressure required to meet the heating requirements of the incoming air in spite of substantial variations in the outside vair temperature. Furthermore, itis an Vobjectief my invention to provide control means for distributing the `steam supplied between the preheatirigl and reheating radiators as required, while allowing differing pressures to be maintained within the preheating and reheating radiators as needed to balance the heating carried out by the two types of units. More specilically, it is an object of my invention to provide control means by which steam can be incrementally supplied at the pressure required to meet the needs of the Whole system and then redistributed within the system to meet the varying needs of the reheating and preheating radiators. Also, it is an object of my invention to provide means for the more efncient utilization of exhaust steam by theI radiation units. Further objects and advantages Will appear as the specification proceeds My invention is shown in an illustrative embodiment in the accompanying drawing invwhich is shown atypical forced air heating systemkof the tunnel-type in diagrammatic side view employing the control means ofvmy invention For purposes of simplied'explanation, my new control means will be described Aprimarily in connection4 with the tunnel-type of forced air heating apparatus. However, I wish it clearly understood that I do notlimit the applicability of my control means to this specific type of forced air heating apparatus. VFrom the following discussion, itv will be clear that my control means is generally applicable for use in connection with any forced heating apparatus of the class wherein cold air is fan-supplied to an enclosed heating zone invvhich the air is first preheated to a selected temperature and then further reheated to a higher distribution temperature by steam radiators; Inithe illustration given, ID designates a heating zone in the formof a tunnel. At one end, tunnel I0 is in direct communication with a fresh air shaft H through which cold fresh air is supplied from the outdoors. In the illustration given, and preferably,` a corridor air return I2 is provided to supply recirculated air to combine with the fresh air introduced at the mouth of tunnel I0. y It will be understood that the proportion of fresh air to recirculated air can be varied as desired by mixing dampers, etc. (not shown). In actual operation, in buildings such'as schools, the volume ratio is frequently maintained at about one to one between fresh and recirculated air.

At the mouth of tunnel Ill there is provided two preheating radiators, the first preheater being designated as I3 and the second preheater as Il. It will be understood that preheaters I3 and I4 are provided withopenings or apertures therethrough for the passage of air through these heating units into tunnel I0. Also, two preheaters are generally usedin forced air systems 7 ofi this.' class-and itfis-apparentl that: this number can-'be changed as 'desiredso long aswatleast -one preheater is vutilized which has sufiicient heating capacityto'meet thei heating requirements -of the inc omin'g: air,

In the illustrationigivema fan orblower I isf mounted in tunnelxl'infront of preheaters I3. and' I4 morder to movesuch air therethrough. Thus, allof the incoming air atv all times passes through preheating radiators I3 and: I4 in; entering `tunnel Il). Heretofore, a Icy-pass damper 1(not shown) has been provided in a lduct bylpassing.thepreheaters For example,` such a bynpass damper could be .located inplaceof` imperforate'plate I6 in thesystem-shown. However, with-.my nevvfcontrol means the need for a-by- `pass darn-per in lthis position is completely eliminated. `In-installingfmy heating apparatus gof :this type having my control means incorporatedtherein the conventional mixing damper would simply be omitted. InA converting the systems znow A in use to my control means, the mixing damper can simply be disconnected from its thermostatic control sothat it will Vpermanently remain closed.

In the tunnel-type of system a plurality of spacedcompartments or casings I1 are provided .within tunnel I0. In the illustration given, three Ycasings I1 are shown. Casings I1 are so placed in tunnelII) that the forced air from fan I5 travels around and below and a portion thereof into casings I1. In the illustration given, and general1y,casings I1 are composed of metal and are ,not insulated infany way.

V,Within-each casingl I1 there is provided -a dividinge partition I81Whichv separates the interiorof the casing I1-intotwopassages or ducts I9 and 20. Induot lI9 inthe illustrationgiven there is locatedf--twof reheatingradiators 2l. It will be understoodthat reheating radiators 2! are provided with suitable openings orapertures therethrough softhatfthe portionof air passing through ducts `Iipasses entirely through reheating radiators 2|. DuctZO- is yintended tobe a -by-pass ar-ound reheating radiators 2I by-Whichair can be passed .upwardlyf-rom.tunnel I0 through room ducts 22 without passing directly through reheating radiators 2|. In the Aupper portion of casings I1 ducts vIII-and2Il-con'1zmunicatewithroomduct 22. ,How-

every-a mixing damper 23 is provided to regulate theproportion of reheating and by passed airintroduced into room ducts 22. In the illustration given mixingdampers 23 consistV of two leaves Hwa-nd 23h linked by member 23a so that when leaff23a, is-movedtowards closed position leaf 23h-` moves towards open position. By this arrangement, the volume of heated air deliveredto room-ducts'22 is maintained substantially constantwhile allowing for -the variation in the proportionof reheating air to by-passed tempered air. Mixing ydamper 23' can beoperated by any convenient motor means In the Villustration given,landgenerally7 damper 23 is'operated by suitable linkage to an-air motor 23, which is actuated by an air supply pipeV` 25 which communicates with thermcstats (not shown) located in the rooms to be heated to which air is conveyed by-room ducts 22.

In `:the .illustration given for purpose of clarity,

thesteam supply pipe, condensate returnY pipes and-other piping is shown below tunnel Ill. *Howeveryit will kloe understoodthat in actual installations such pipingis'usually` installed Within tuni f .the illustration.: given; a.. steam. supply pipe '26is shown. Itiwilltbe understood-:thatlthe'fstezm -within pipe :.26 can Vbe f suppliedy fromzanytcon.- venient source such as -a steam boilerfandthat it,` can be atV either 4h-igh ,or. low pressures. that is, from. one to three to one-hundredandtwentyfive pounds per `squareiinchgauge. ...I prefer. however, `to' utilize-,steam at relatively `high pres.,- suresfoflarcund one-hundred p. s. i.;g. or somewhat in-excess thereof. Steam-supply maint-26 is connectedto thepreheating radiatorsloyy pipes 21-and.to the reheatingradiators Ibyspipes 28.

It Will be noted as is generally the case, that Preheating radiators I3- and |14 and reheating rad-iators l`2 I are -all connected in parallelto steam sup'- ply main26. y

ra-:condensate return pipe 29: isprovidedfrwhich is connected'to the oppositeend.ofppreheating radiators I3 and t4 by pipe=30 and -to theopposite end Qf'reheating radiators :2Ifand Vpipes-3L -fA condensate return pipe 29 isf preferably-equipped withfa condensate'pump (not shown).1 tofmain.- taina vacuum`suction on the condensate line, althoughr ai ygravity return can: be utilized.

The apparatus shown is designed for/@best operation with a steam: supply inf steam-supply main 26Y atfrorn about ten to-onehundredand twenty-ve p. s. i.;g., and a steam pressurewith inV the radiation Vunits at from yone to `'three poundsV prs. i. g. Therefore, a= pressure lregulating valve 32 is positioned inline 26 between: the steam supply source and the juncturefof pipes 21 andZBvr to the Apreheating and reheating radiaf ticnrunits. Pressure regulating -valvef 32A .can beany sort oa pressure regulating valve which eanbe used' to reduce the pressure fromzaboutften to Aone-hundredand twenty-ve p. s.- i.L gx on' vthe boiler side toV fromzoneto three pounds on, fthe radiation' side of the system.Y In theI illustration given, pressure regulating valve 32 -is-argate'valve equipped with a diaphragm4 33f-.which is connected by pipe-Sito the radiation'side ofgspipe 2S. :Since the z construction of such diaphragme-controlled pressure s regulating Y valve is well-known, s it is believedV that it will not be necessary to. further describe it herein. I prefer to 'utilizea; pressure regulatingvalve which can be set `for-varying pressures as desired, suchfas by Weight Aload'- ing in :valves of the pressure-diaphragm type.

Thesupply of steam is further controlledbyfa motor-operated, gate Yvalve 35. ,Gate/valve 351can be, anytype ofv motor-operated valve `which-ris capable of.=being controlled by a thermostat and moved over a range of Apositions 'from closed; to fully open. In theY illustrationl given, va1ve35 isl actuated bya diaphragm member 3which is connected by. an air supply line 31 to thermostat 38.

Thermostat 38 can be located at any VVpoint at Which `it 'canr measure the tempered' air .temperatures andib'eresponsive thereto. Preferably,

thermostat 38 is located close vto the voutputside.

of fair I5 so thatit can be immediately'responsive 'to changes in the temperature ofthe tempered air produced by preheaters I3 `and vIll andA passed into tunnel 'I9 by fan I5. It will be understood from what has been-said in connectionzvvithV the structure of valve '35,that thermostatV 38 is to be selected so that it can actuatefvalvei. p Thus, if vvvalve V35 were to be electricall'yeoperated thermostat 33 should be an electrical-type ther.- mostat. In the illustration given; thermostat'138 is ofthe air pressure typehavingza le'ak lport39 through which air supplied by line 4D can escape whenl the leak' port .begins to: open. Sincetthe structure: thermostatsotlthis characterlis `'wellknown it is not believed that it will be necessary to further set out such structure herein. The method of operation of such thermostats is that a selected pressure, say p. s. i. g. is normally maintained within pipes 31 and 40. However,

when the temperature of thermostat 38fdrops` below a selected value, say '70 F., the leak port 39 begins to open and thus reduce the pressure within line 31. Leak port 39 generally continues to open over a temperature interval, which generally is around two degrees until fully open when the pressure in lines 31 and 40 is reduced to zero p. s. i. g. Diaphragm 36 has a spring exerting force on one side thereof which would be effective in opening valve 35 if it were not for the air pressure within pipe 31. This spring can be of any selected strength less than the pressure of the air supply. Thus, if the spring pressing against diaphragm member 36 is ,of ten poundsl strength, valve 35 will not begin vto open luntil the pressure within line 31 is reduced to ten poundsby the leaking of air through leak port 39. s

Motor-controlled gate valve 3Ecan be located either above or below pressure regulating Valve 32. Also, gate valve` 35 andpressure regulating; valves`32 can `be combined through one valve which` is adapted to perform both functions. The structure of such yalves'is well-known to those skilled in the art, and they are readily available' from valve manufacturers. I prefer, however, to either use a single valve to accomplish the functions of valve 35 and pressure regulator 32 or to locate valve 35 above pressureregulator 32, as shown in the drawing. This arrangement of valve 35 is preferable because the full boiler steam pressure is available to incrementally inject steam intothe radiation system.` `This method of operation will subsequently be `mcre'fully described. In pipes 421 I provide motor-operated gate valves 4I, which are preferably of the saine `type as gate valve 35 in order that gate `valves 4I can also be controlled by thermostat 38. If desired, however, separate thermostats located `near thermostat 38 can be used to control valves 4I. In the illustration given, gate valves 3l are controlled by diaphragm members 42 which are connected by air pipes 43 to line 31,. It will be understood that `diaphragm structures can be made to operate in the same wayas diaphragm member 36,` which method of operation. has been fully covered above. It will also befunderstood that the springs within diaphragm members 42 can be of different strengths and thereforeV opening or beginning to open valves 4I at different pressures from each other or from valve 35.

"I also prefer `to equip the steam supply qlines to the radiation u nits with manually operated gate valves which can be used to uallow steam to bypass the motor-operated valves and lto cut in or outV a particularI radiation unit. .In the illustration given, these functions are performed by by-pass gate valve 44 located in by-pass line 45 around motor-controlled valve 35. Similarly manually-operated gate `valves `46 are located in by-pass lines 41 around motor-controlled` valves 4I. Adjacent to preheaters I3 and I4, pipes 21 are also equippeddwithmanually operated gate valves4 48 by means of which preheaters I3 and I4 can cut in and outof the steam circuit. Likewise, preheating radiators `2 I are individually equipped .with manually operated gate, valves `49 which can be used to cut them in or out as desired. s v V `j I also `prefer to provide a pipejI) communicat- `suitable butterfly valve to prevent the backow or steam within pipe 50.

The operation of my control means which consists essentially of motor-controlled valves 35 and 4I and thermostat 39 can best be appreciated by reference to a specific example. However, I wish it clearly understood that this example is merely set out by way of illustration and not limitation, since my control means can be adapted for use with other types of forced air heating apparatus in which it is desired to eiect a distribution of steam by the preheating and reheating radiators within the plenum chamber.

EXAMPLE The general operation of the control system 0l' my invention is to arrange the valves and to provide for their automatic operation so thatany excess steam within reheating radiators 2| which is not required `to meet the secondary heating needs can be redistributed to!` preheating radiators I3 or I4 before additional steam is supplied to both the preheating and reheating radiators from the steam supply main. Whenever additional steam isrequired, it is intended that my control means be operative to supply such steam requirements incrementally at pressures` corresponding with those required to maintain the selected preheated air temperature. Further-` more, it is intended to provide a` 'structure` in which exhaust steam can be introduced into the radiation units to supply` their heat requirements such as by pipe 50. ,Y

It will be assumed that the forced air heating apparatus shown in thedrawing is to be used to heat the rooms of a school building in which room ducts 22 supply at least one room with heated air. It will be further' assumed that thermostatic controls are located within these rooms to actuate mixing dampers 23. s While this control system can be of any suitabletype, the` illustration given showns an air `pressure control system, since this type of control system is usually found already installed in school buildings at the present time.

Generally, it is desired tomaintain room temperatures of about F., which requires that air be delivered to the room at from '14 to 150 F. depending on the weather conditions and outdoor temperatures. It will here be assumed that the outdoor temperatures are around 40 F. andthat to maintain the desiredroom temperatures `of 70 F. that the air mustbe deliveredto the rooms at about F. Y To achieve this result, thermostat 38 is set to begin to open leak port 39when the temperature of the tempered air falls below 70 F. and to continue to reduce the pressure in air lines 31 and 40 untilra zero pressure is attained at` about 68 F. Air is supplied into lines"'31 and 40 at approximately 15 p. s. i. g. `Diaphragm motor 36 is set to begin to open main valve 35 at about 69 F. or 8 p. s. i. g., lwhile diaphragm motor 42 is set to open the first preheater V,I3 valve 4I` at about 69% F. or 10 p. s. i. g. and the other diaphragm motor 42 is set to begin to open valve 4I for the second preheater I4 at about 68% or 6 p. s. i. g.

The effect of setting the valves in this manner can best be seen by looking at the Typical Operational Chart, set out onthe following page. I

` 'Twice-Pedim? Chart Operation Thermostat Controlled Valves f lherrvnosttsetting -v l' Y 1 1 V Main Line Supply First Preheater Second Prelieate;

7ejposrp, 5.1. g.) y muy @10ste 'Y muy closed Fully Closed. 69F. V(10p. s. i. g4) l v Begnsrto Open 69 F. (8 p. s. i. g.).... Begins to Open zgy'FuLp. s.vi..g.;..v Begins tQDpen.

, v v I Y p l l 1 l T GB FJ() p. s. i, g.)y.. Fully O peu Fully Open Fully Open v In addition'to they-settings mentioned above 2Q valve?iw-angll'st'pxjeheateg-valve!!!until'these apdsetfout ILthe chart, pressure regulating valve 3g Wis: 4vset athe,Inaiiuu'rrn pressurefwhich will be requiveilwitliin the,radiation` units to -nieet the he greguiifementsgof theincoming airv at its lo".l 4probablelterr'xperature; For` example, in the j lllustratidj fgiverli `this pressure regulator 3 2 islse a 3;p`fA s'. i; g. Thus; pressure Vregulator 32 Wi jop'enuntilja pressure is nbuilt up Vin egce ns A v3` prQuIidS p; sri. 'gg Within the radiation unitSn-M l Y "Re exjririg novvjto the operational chart setout app; 'e aftypial-jcyleofjopeiations at the 'indi- Cat`"settings`wil1be explained; 'At tempered air Y tions just described i e 11y repeatedas di'' rectedbytherte ure r mentspf the ,Y omnatempeled warm weather .the temperaturetpterialjbetween. t iielieat'er' valve arid 'the ondpzeheater vfalve'fd l` begins 4penas. indicated onthegchaxt. Steam lsthengntr'oduced intogthe second preheating' unit which doubles the y p itethe opening .of the presxurle'to the ra 13 decreased. Under comparable conditions, it has been found that fuel consumption can be cut from 15 to 20% .or more.

While in the foregoing speciiication I have set forth specic structures and operating conditions for the purpose of illustrating an embodiment of myrinvention. it will be apparent to those skilled in the art that many of the details of the conditions specified can be widely varied without departing from the spirit of my invention.

i I claim: t

.1. In a forced air heating apparatus of the class described wherein cold air is fan-supplied to an enclosed heating zone in which said air is rst preheated to a selected temperature and then further heated to a higher distribution temperaturei by steam radiators, said apparatus including apreheating radiator and a reheating radiator connected in parallel by branch pipes to asteam supply main and having condensate return pipes attached thereto, the combination with said apparatus of a motor-controlled gate valvetmeans in said supply line together with a pressure regulating means, both of said means being located above the juncture of said branch pipes so as to control the imput `quantity and pressure of steam to both of said radiators, a motor-controlled gate valve means in the branch pipe between said supply main and said preheating radiator to separately control the supply of steam to said preheating radiator, and a thermostat control means responsive to variations in the preheated air temperature actuatingv both of said motor-controlled valve means, said thermostat means being set to open'and close both of said valve means over narrow overlapping temperature ranges and to begin to open said preheater valve means at a slightly higher temperature than said supply main valve means, whereby excess steam in said reheating radiator can be distributedrto said preheater radiator before additional steam is supplied to both of said radiators by said supply main valve means and when additional steam is required said steam is supplied incrementally at pressures corresponding with those required to maintain the selected preheated ar temperature.

2. In a forced air heating apparatus of the class described wherein cold air is fan-supplied to an enclosed heating zone containing steam radiators in which zone said air is rst preheated to a selected temperature and then further heated to a higher distribution temperature, said apparatus including two preheating radiators and a plurality of reheating radiators beingl connected in parallel by branch pipes to a steam supply main and having condensate return pipes attached thereto, said apparatus also including a by-pass duct around said reheating radiators equipped with a mixing damper to control the temperature of the distributed air by varying the proportions of reheatedand by-passed preheated air, the combination with said apparatus of a motor-controlled gate valve means in said supply line together with a pressure regulating means both of said means being located above the juncture of said branch pipes so as to control the imput quantity and pressure ofsteam to all of said radiators, a motor-controlled gate valve means in each of the branch pipes between said supply main and said preheating radiators to separately control the supply of steam to each of said preheating radiators, and a thermostat control means responsive to variations in the preheated air temperature actuating all of said motor-controlled valve means, 'said thermostat means being set to open and close all of said valve means over narrow overlapping temperature ranges and to begin to open one of said preheater valve means at a slightly higher temperature than saidisupply valve means and theother of said preheater valve means at a slightly lower temperature than said supply valve means, whereby excess steam in said reheating radiators can be distributed to one of said preheating radiators before additional steam is supplied to all of said radiators by said supply main valve means and when additional steam is required said steam is supplied incrementally at pressures corresponding with those required to maintain the selected preheated air temperature, said additional steam being rst introduced into one of said preheating radiators and later into the other of said preheating radiators according to the heat requirements of the incoming air.

` 3. In a forced air heating apparatus of the class described wherein cold air is fan-supplied to an enclosed heating zone containing steam radiators inwhich zone said air is rst preheated to aselected temperature and then further heated to a higher distribution temperature, said apparatus including two preheating radiators and a plurality of reheating radiators beingconnected in parallel by branch pipes to a steam supply main and having condensate return pipes attached thereto, said apparatus also including a by-pass duct around said reheating radiators equipped with a mixing damper to control the temperature of the distributed air by varying the proportions of reheated and by-passed preheated air, the combination with said apparatus of an air motor-controlled gate valve means in said supply line together with a pressure regulating means both of said means being located above the juncture of said branch pipes so as to control the input quantity and pressure of steam to all of said radiators, an airA motor-controlled gate valve means in each of the branch. pipes between said supply main and said preheating radiators to separately control the supply of steam to each of said preheating radiators, and an air pressure thermostat control means responsive to variations in the preheated air temperature actuating all of said motor-controlled valve means, said thermostat means being set to open and close all of said valve means over narrow overlapping temperature ranges and to begin to open one of said preheater valve means at a slightly higher temperature than said supply valve means and the other of said preheater valve means at a slightly lower temperature than said supply valve means, whereby excess steam in said reheating radiators can be distributed to one of said preheating radiators before additional steam is supplied to all of said radiators byv said supply main valve means and when additional steamis required said steam is supplied incrementally at pressures corresponding with those required to maintain the selected preheated air temperature, said additional steam being rst introduced into one of said preheating radiators and later into the other of said preheating radiators according to the heat requirements of the incoming air.

4. In a forced air heating apparatus of the class described wherein cold fresh air is fan-supplied to a tunnel containing steam radiators in which tunnel said air is first preheated to a selected temperature and then further heated to a higher distribution temperature, said tunnel including a preheating radiator at the mouth ingradiator, to= separately control thesupply ofV steamfto said preheatingradiator, and'athermostat control means responsive to rvariations l in theipreheated airtemperature actuating both of Y said-i motor-c'ontrolledV valve means, :said thermostat means being-:setto openl and close both of said valveymeansover narrow overlapping tem-I perature ranges and tobegin toV open said preheaterfvalve means ata slightly higher temperature; than said supplyy main valve: means, whereby excess Y,steam in said reheatin'g vradiator can be distributed tosaid -preheater radiator -before additional-steam `is suppliedto both of said vradilili atersfbysaidisupply-main valvefmeans. and when Y additional steam is required said-steam is ,supplied incrementally atpressures corresponding with these requiredftoamaintain the selected preheated air-temperature v,

E .nln a forcedfair :heating apparatus of the classV described wherein coldrfresh.l air together withxreeirculated air islam-.supplied to a heatingtunnel-containing twov-preheating radiators 5,-.,-`

atthemouththereofV through which said air is causedto pass andfa plurality. of reheating radiatorsjlocatedE-in casingsrwithin said. tunnel, said casings providing-a by-pass duct therein around saidf-:reheating radiators equipped with a mixingidampertocontrol thetemperature of the distr-ibutedfaiaby .varying the proportion of reheatted and=bypassed preheated air,y the combi-V nation with said apparatus of a motor-controlled gate value, means in said supply lme to-` getherwith a pressure regulating means both of` saidmeans beinglocated above-the juncture .of said ,branch pipesfsofas to ,control-the imput. quantity'andv pressure `ofstearn, to allv of4` saidy radiators, a motor-'controlledgatevl valve. means ineachrofv the branch pipes between saidsupply. manQand -said .prensa-,ting .radiators to separately controlithevsupplyof rsteam to eachlof said preheating rradiators, anda thermostat control means responsive f-to variations .in the Vpreheated. air., temperaturef actuating all of ysaid motor-l controlled valve. means, said thermostat meansV being settoopen and close all ofsaid valve. means over Inarrow overlapping. temperatureranges and. tobeginpto `opencnejof said preheaterrvalve means, at a slightly higher temperature, than said supplyvalvenieans andthe other o said preheatei; valve meansiatja slightly lower temperaturevthan said supply valve' means, whereby excess steam :in said reheat-ing. radiators can be f distributedtooneofssaid.preheating'radiatorstbee fore iadditionalsteamzvvfisfsuppliedv.to 1 alla: ofi said radiators by said supply main .valve Ameans and when additionalsteamf istrequireda said.ste'auril "s supplied:incrementally pressures :correspon-dri ing` withizthoses required to'maintain 2- theaselectedi preheatedlairr temperature, saidadditional steaml being rrstintroduoed into one of saidipreheatn'gi radiators'accordinglto'V the Fheat r requirements' of the incpmi-ngxairzg: 1 v i l L;

6. In a forced air heating apparatusofl the class;.describled" wherein cold afresh air together withrec-ircuiated airfisian-supplied toi arheating:

tunnel: ,containingr two preheating radiators-5 atY i the mouth thereof through which said iairais;

caused to pass and a plurality of relocating-radiators located in fcasings, within saidv tunnel; said'casings providing a by-pass duct :therein: around .said .reheating radiators equipped withI a. mixing damper to control, theV temperature of: thedistributed air'by varying the proportion of reheated and by-passed preheated air, the com-v bination with said apparatus of an airV motor-l controlled gate valve means in said supply line I together Awith apressure Vregulating means bothof saidmeans lbeing located above the junef ture of said branch pipes so as to control thev inputwquantity and pressure of steam toV all-yor Y said radiators, an air motor-controlled gate valve means in each of the branch pipes vbetween said supply mairrand said preheating radiators to. separately control the .supply ofA steam topf-each.l of said preheatingY radiators, andan air-pressure-thermostat control means responsive to var.- iations in the preheated air temperatureactuatall of said air motor-eontrolledvalve means,A thermostat means being set to open and close all of said valve means over narrow overlapping temperature ranges and to begin-to openone of said preheater valve meansat aslightly higher temperature'than said supply valve means and; the other. of said preheater valve means ata slightly lower temperature than said supplyvalve meanswhereby. excess steam. in said reheatingA radiators can be' distributed to one of saidlpreheating radiators before Aadditional steam is supplied to all of vsaid radiators lbyf said supply maintvalve means and i whenv additional steam is required said. steam 'is supplied `'incrementally atrpressures correspondingwith ths'evrquired to maintain theselected preheated "air temper:

ature, said additional steamf being first l intro-. ducedlinto one of said preheating'radiators ac- CHARLES lW. CARrLsoNzf anraanNcEsfCrrEn Thefollowing-references*are of record.r in the; ile oivthispatent: l

UNITEDSTATES PATENTS Numbeiw' NameY Y Date. Rell9q9ll Ewald Apr'."7,1 936" 961,73'4' Powers V Junel 14';V i910 

